1. Field of the Invention
This invention relates to wireless communication devices capable of communication with existing wireless communication networks as well as with wireline networks.
2. Description of Related Art
Wireless communication networks typically include a plurality of specified cellular service areas through which a wireless phone, or mobile station, may pass while engaging in a conversation. As the mobile station leaves one cell area and enters another cell area, the wireless communication network must hand off control and data traffic channels to the new cell area base station.
Cordless telephones, on the other hand, tend to be simpler and require less sophisticated control and management. Typically, a cordless phone is designed to communicate only with its base unit. If a cordless telephone travels beyond the range of the base unit, the call is dropped. The ongoing conversation is not handed off to another base unit.
As a part of the Personal Communication System ("PCS") being developed in tested in various areas, there is a desire to develop a wireless dual use phone system that is capable of operating both as a cordless home phone and as a wireless mobile station capable of communicating with wireless communication networks. As the design of such dual use telephones progresses, however, several problems with implementing such a system are being discovered.
Under the PCS network, mobile stations are operable with 1900 megahertz (MHz) frequency band. The newest technology cordless phones, however, are operable in the 900 MHz frequency band. One known advantage of using 900 MHz as the operating frequency for a cordless phone is that a signal at 900 MHz may readily be propagated throughout a small structure such as a home or office more readily than prior cordless phone systems that operate at lower frequencies. The signal quality and resulting voice quality is improved in relation to many previous cordless phone systems.
As a result, current design effort includes developing dual use phones operable to communicate both with a base unit within the home and with a base station of a cellular communication network. Relating to the 1900 MHz systems that are being developed, however, it has been discovered that obtaining proper coverage throughout the home or small office in which a cordless phone is operating at a 1900 MHz frequency band. It has been found that a signal operation in the 1900 MHz frequency band does not propagate well throughout a house or small office if the cordless phone's base unit antenna, which is structurally coupled to the base unit, is kept at or near ground level. Because base units are operable not only to communicate with the cordless unit and the public switched telephone network ("PSTN"), but also to charge the batteries of the cordless phone, base units are kept at or nearly at ground level so that the base unit remains accessible for receiving in the cordless phone to recharge its batteries. Thus, current design proposals for dual purpose phones operable at a 1900 MHz frequency band for communications with base stations as well as with base units is problematic.
Accordingly, several design proposals have been urged for PCS based dual purpose phones to overcome the known signal coverage area problems which exist for 1900 MHz transmissions. One proposal is to use dual purpose phones which communicate with the cellular base stations at a frequency of 1900 MHz and which communicate with the base units of the phone at a lower frequency, by way of example, 900 MHz. One drawback to this proposal, however, is that a mobile station or phone must include additional circuitry to communicate with both types of phone systems at two frequency bands, namely, 900 MHz and 1900 MHz systems.
Another proposal is to place the base unit antenna for communication with a dual purpose phone above the ceiling in an attic or the like. The coverage area for a 1900 MHz system can be improved by raising the elevation of an antenna of a base unit operable at 1900 MHz. Accordingly, it is thought that the antenna could be removed from the base unit of the base terminal and could be connected to the base unit by a coaxial wire. A problem with placing the antenna in an attic or other raised elevation, however, is that a large coaxial cable must be used to carry a 1900 MHz signal as a result of cable attenuation resulting from these frequencies. By "large", it is believed that a cable with approximately a 3/4 inch diameter must be used.
Using such a large coaxial cable is problematic for several reasons. First, 3/4 inch coaxial cable tends to be very rigid and difficult to work with and difficult to route from one point to another. Secondly, and perhaps more importantly, 3/4 inch coaxial cable is aesthetically unappealing. Few people would not complain about having a 3/4 inch cable stapled to a wall and running up into a ceiling. It appears, therefore, that placing an antenna in an attic or at an adequate height to facilitate 1900 MHz communications with a cordless phone or mobile station is a difficult solution. What is needed, therefore, is a system that supports the design and used of dual purpose phone, namely PCS cellular and cordless, which dual purpose phone operates at a frequency of 1900 MHz and which avoids the noted problems that exist for current and proposed systems.